Research in this section consists of studies on the physical and chemical properties of proteins of biological interest and the roles of ligand binding and protein-protein interactions in enzyme catalysis and regulation. (1) Interactions of divalent cations, substrates, and inhibitors with glutamine synthetase from E. coli have been studied by microcalorimetry, equilibrium dialysis, pH, spectral, and kinetic techniques. A reversible thermal transition in the enzyme structure is also being studied. In addition, a specific labeling of the catalytic sites of the glutamine synthetase dodecamer has been achieved by reaction of this enzyme with pyridoxal phosphate, followed by borohydride reduction of the Schiff base. The pyridoxamine phosphate group acts as a spectral probe for the interactions of the modified enzyme with ligands. (2) To produce a specific agglutinating activity, polymerization reactions of IgG antibodies are being studied. BIBLIOGRAPHIC REFERENCES: Caban, C.E., and Ginsburg, A.: Glutamine Synthetase Adenylyltransferase from Escherichia coli: Purification, Physical and Chemical Properties. Biochemistry, 15, 1569-1580, 1976. Shrake, A., Powers, D.M., and Ginsburg, A.: Calorimetric and Equilibrium Binding Studies of the Interaction of Substrates with Glutamine Synthetase of Escherichia coli. Biochemistry. 1977 (in press).